Emergency lighting system AC line voltage sensing

Abstract

An emergency lighting system includes a high reactance transformer with a primary winding for connection to AC line voltage and a secondary winding. Circuit means are provided for monitoring the AC line voltage and includes means for coupling the transformer secondary winding to a non-linear load, a battery, during one AC half cycle and means for coupling the secondary winding to a linear load during an alternate AC half cycle to provide a DC voltage proportional to the AC line voltage.

What is claimed is: 
     
       1. In an emergency lighting system having a high reactance transformer with a primary winding adapted for coupling to an AC energy source and a secondary winding, circuit means for monitoring the AC source voltage comprising: means for coupling the secondary winding of the transformer with a non-linear load during one half cycle of the AC source voltage; and   means for coupling the transformer secondary winding with a linear load during an alternate half cycle of the AC source voltage to provide DC voltage proportional to the AC source voltage.   
     
     
       2. The circuit means of claim 1 wherein the transformer secondary winding is center-tapped. 
     
     
       3. The circuit means of claim 2 wherein the means for coupling with a non-linear load includes a diode connected serially with a battery between a first leg of the secondary winding and the center tap for charging the battery. 
     
     
       4. The circuit means of claim 2 wherein the means for coupling with a linear load includes a diode connected serially with a capacitance between a second leg of the secondary winding and the center-tap, and a resistance connected in shunt with the capacitance, the DC voltage proportional to the AC source voltage appearing across the resistance.